What cam to use in a 318

Hysteric said

I'll never understand why Mopar guys still use 3/8 valves. What's the length of those valves by the way?

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The length is fairly close to the Chev and Ford valves. The advantage of the LS valves is low cost and the 8mm stems keeps the weight down. 8mm is about 0.002" more than the Magnum valve stems but I bet the Chev cost less. You could install Magnum valve guides and hone them to get valve stem to guide clearance just right, kind of along the line of file fit rings.
The next important topic is spring installed height. On the early Ford 289 heads (my 1966) the installed height is 1.65", so the Chev beehive springs will not work. Most of the later SBF heads are 1.78" to 1.79" installed. Close enough to the Chev 1.8" installed height.
My understanding is the SBM are pretty much using the 1.8" installed height or very close.
So using the Chev valves gives a bit larger valves depending on the heads (other LS have 2.0"I and one has 1.61"E valves) at a pretty reasonable parts cost with the rest of the parts included. You could purchase new valves and then grab 4 matching LS heads on a Pick n Pull sale day from low mileage engines and take the springs, retainers and locks. Probably sell the heads for more than you paid. Get the springs checked and use the best 16.